Fifteen years ago the program in immunology of this laboratory was initiated. Its long-term aim has been to gain as complete a knowledge as possible of the events that transpire during the differentiation of B lymphocytes. It has become evident that the events of this immunodifferentiation program, as mirrored in alterations of immunoglobulin gene structure, are a reflection of changing patterns of gene transcription. The program therefore now emphasizes the study of individual transcription factor proteins that we had earlier identified as crucial to the expression of immunoglobulin genes. In particular, it is focused on three such factors, NF-kappaB, the helix-loop-helix proteins E12 and E47, and Oct-2. NF-kappaB is the key factor for the activity of the kappa gene intron enhancer. Its subunits are members of the rel family of proteins and its activity is controlled by members of the ankyrin protein family . It is planned to use monoclonal antibodies and gene knock-out strategies in mice to understand the roles of the individual family members. To examine how NF-kappaB becomes constitutively active in B cells, the phosphorylation state of its inhibitor, IkappaB, will be determined. The structure of the Rel domain will be studied in a collaborative effort. The E12/E47 proteins are part of a family and, again, antibodies and gene knock-outs will be used to distinguish among them. The possibility of a B cell-specific member of the family will be investigated. For the Oct-2 factor, found preferentially in B cells, the question is why it is present. A knock-out of the gene has produced no obvious alteration in B cells. The possibility that exists to avoid cell-cycle regulation of immunoglobulin synthesis will be investigated. A major focus will be the use of in vitro analysis to examine the roles of the various factors. This work will encompass not only the three mentioned factors, but others that control the kappa light chain gene. Silencing of transcription is as important as activation. Recent evidence suggests that the many B1 repeats of the mouse genome may serve a silencing function. This has been seen in the kappa light chain gene and the T cell receptor alpha gene. The generality of the phenomenon and its mechanism will be studied.